J.C. Belchior

Global optimization analysis of water clusters (H2O)n (11⩽n⩽13) through a genetic evolutionary approach

The structures and stabilities of water clusters (H2O)n with 11⩽n⩽13 are determined by a genetic algorithm approach with two new evolutionary operators—namely annihilator and history operators. These studies show that the modified genetic algorithm provides an efficient procedure for calculating global minima with an especial attention to molecular water clusters. The actual results are in quantitative agreement with previous calculations using the basin hopping Monte Carlo method.

Structural and energetic analysis of copper clusters: MD study of Cu n (n = 2-45)

Molecular dynamics simulations, via an empirical potential, have been performed in order to investigate geometries, growing patterns, structural stabilities, energetics, and magic sizes of copper clusters, Cun (n = 2-45). Possible optimal stable structures of the clusters have been generated through following rearrangement collision of the system in fusion regime. This process serves as an efficient alternative to the growing path identification and the optimization techniques. It has been found that copper clusters prefer to form three-dimensional compact structures in the determined configurations and the appearances of medium sizes are five fold symmetry on the spherical clusters. Moreover, relevant relations between atomic arrangements in the clusters and the magic sizes have been observed. Cu26 may be accepted as another putative magic size like Cu13.

Spherical potential energy function from second virial coefficient using Tikhonov regularization and truncated singular value decomposition

Abstract The inverse problem to determine the potential energy surface from the second virial coefficient data, involves the solution of a discrete ill-posed problem. The Tikhonov regularization and the truncated singular value decomposition methods, which are appropriated to handle ill-conditioning linear system, were applied in this work to obtain the potential energy surface for an atom-atom short range interaction from second virial coefficient.

Artificial neural network applied for predicting rainbow trajectories in atomic and molecular classical collisions

A simple artificial neural network (ANN) is developed and applied to collision processes. A general discussion of how ANNs can be introduced to study general phenomena in scattering problems is presented and neural networks are proposed to predict classical rainbow trajectories in atomic and molecular collisions. As a result of modeling the collision process, based on the neural network approach, analytical equations were obtained to calculate classical atomic and molecular rainbow trajectories. However, these analytical results just translate the behavior of the input/output data and do not contain any general physical meaning. Although a fitting procedure could be easily used in the present case, the cost of function approximation using ANNs increases only linearly with the number of input variables. This contrasts with classical polynomial fitting procedures for which the computational cost increases exponentially with the input space dimension. This makes the ANN approach worth considering when modeli...

Experimental and theoretical studies of the thermal behavior of titanium dioxide-SnO2 based composites.

In this paper we report experimental and theoretical studies concerning the thermal behavior of some organotin-Ti(IV) oxides employed as precursors for TiO(2)/SnO(2) semiconducting based composites, with photocatalytic properties. The organotin-TiO(2) supported materials were obtained by chemical reactions of SnBu(3)Cl (Bu = butyl), TiCl(4) with NH(4)OH in ethanol, in order to impregnate organotin oxide in a TiO(2) matrix. A theoretical model was developed to support experimental procedures. The kinetics parameters: frequency factor (A), activation energy, and reaction order (n) can be estimated through artificial intelligence methods. Genetic algorithm, fuzzy logic, and Petri neural nets were used in order to determine the kinetic parameters as a function of temperature. With this in mind, three precursors were prepared in order to obtain composites with Sn/TiO(2) ratios of 0% (1), 15% (2), and 30% (3) in weight, respectively. The thermal behavior of products (1-3) was studied by thermogravimetric experiments in oxygen.

Hopfield neural network model for calculating the potential energy function from second virial data

Abstract The calculation of the intermolecular potential from the second virial coefficient is treated here by using a Hopfield neural network model. From simulated data for the prototype system HeNe, the repulsive potential was obtained with a desired accuracy. The algorithm used here is general, as it can handle noise in the experimental data and, a neural network of higher dimension can be easily constructed. Although the inversion of the short-range part of the potential was obtained in the present work, the Hopfield neural network under consideration can equally be used to invert virial data to give the long-range part of the potential. The convergence of the states of the neuron and the accuracy of the inverted potential is also discussed.

Artificial neural networks applied for studying metallic complexes

Metallic complexes of multimetal and multiligand systems are complicated for calculating equilibrium concentrations in solutions. An artificial neural network has been developed for studying Al3+ and EDTA complexes in solution with an initial concentration of 0.01 mol L−1 for these species. In this system there are 20 compounds and may exist 18 simultaneous reactions. The neural network has been trained and the simulated data of different concentrations as a function of pH are predicted with an accuracy of about 1% for all species simultaneously. A general analytical formula is presented, which directly relates all the concentrations as a function of pH. The analysis showed that predictions closer to the boundary of the input and output data are quantitative while out of these limits these are not even qualitative.

A critical analysis of the two-dimensional atom ellipsoid model to study rotational collisions

Abstract The two-dimensional (2D) hard ellipsoid model is criticized and the calculations are compared with the 2D classical trajectory results. The scattering angle θ and the final j for a set of initial conditions (α and b ) have been analyzed and it was concluded that the contribution of ∂j / ∂α is the leading term in the Jacobian function. Moreover, the rainbow trajectory calculated by the hard ellipsoid model turned out to be highly accurate for low scattering angles and semi-quantative for the maximum rotational rainbow. For the latter, a relative error of about 10% has been found compared with classical trajectory results. Finally, an inversion procedure based on such a model has also been re-analyzed and better information on the anisotropy of the interaction potential was found using an exact equation rather than an approximate formula for the hard ellipsoid model.

A comparison of state-to-state rotational total cross sections using two- and three-dimensional close coupled approaches☆

Abstract State-to-state rotational cross sections have been calculated for the XeCO2 scattering at 0.01 and 0.03 eV collision energies using the two- and three-dimensional close coupling methods. As will be pointed out, these results are in fair agreement only after the last multiple collision maximum in the two-dimensional dynamics. The full two-dimensional quantum total cross sections, at 0.2 eV of the collision energy, are also presented for the collision process under study.

Coordenadas cartesianas moleculares a partir da geometria dos modos normais de vibração

A simple method to obtain molecular Cartesian coordinates as a function of vibrational normal modes is presented in this work. The method does not require the definition of special matrices, like the F and G of Wilson, neither of group theory. The Eckarts conditions together with the diagonalization of kinetic and potential energy are the only required expressions. This makes the present approach appropriate to be used as a preliminary study for more advanced concepts concerning vibrational analysis. Examples are given for diatomic and triatomic molecules.